day 1 : 48 hours after tap water, ph still fluctuates although not catastrophically. around 6.2 this morning then correction after correction now its 5.5 after addition of biogrow to make 2ml/l because its like light mix I guess. Or even more I think I can give because I think the leaves are showing signs of lack of nutrition (palish outskirts of older leaves). Other than that, roots are showing up in all 4, the upper left late obviously.

day 2 : called shop : they said the water ph with tap water will always rise. no matter how much acid you put. So I think that the viable solution would be distilled water. and maybe try another type of acid. (nitric acid? )
the leaves of chronic the lower ones are decaying (is it really like from carence?, ph seems around okay, EC too, temperature okay, no pest. So probably it requires way more nutrient than I thought.
day 3 : in a desperate attempt to stabilize ph, I shaked the bottle of acid. and put some. and before sleep : 4.2

day 4: wake up : 4.3. wow so the acid bottle shaking actually works!

day 5 : so the ph raise very slowly compared to before. today put no correction. yeah. but checked the roots, they are a bit yellow and the small ones are damaged probably by too acid water for some time. yeah... and the EC raised. to 1.4 from 1.2 instead of going down. so probably the water is taken so quick that the solution becomes so strong.

day 6 : woke up and ph was 6.2. so added a few drops. hope that from now, the ph problem is over. no more too acid, and I know how to reduce the necessity of doing this too often.

note :
next time, try mix water tap and distilled for better pH control.